An alignment device for use with a robot for manipulating and aligning a series of semiconductor wafers with respect to an edge fiducial and the center of each wafer is disclosed. The device includes a rotary vacuum chuck for holding a wafer, and an edge detector comprising a light source that extends across the wafer edge as it moves and creates a shadow that falls on a charge coupled device (CCD) below. Output data from the CCD relative to the wafer edge position is processed by a programmable logic circuit and converted to quadrature data which is fed to the logic section of a controller. The controller is programmed to calculate the location of the wafer fiducial relative to the chuck axis and further to calculate the angular and distance offset of the wafer center from the longitudinal axis of the robot arm so that the robot arm can be moved to center the wafer with its fiducial at a preselected location before the wafer is removed from the rotary chuck.
Legal claims defining the scope of protection, as filed with the USPTO.
1. In a system for manipulating a series of disk like elements so that each element can be transported separately by a robot having an articulated two leg arm and an end effector to a station in a precise, predetermined orientation and alignment with respect to a reference fiducial on the element edge and the geometric center of the element, said system comprising: (a) a machine controller; (b) a rotary vacuum chuck for supporting an element and having a motor for driving said chuck connected to said controller; (c) an alignment device including an elongated light source which is above and extends across the outer edge of said element held on said chuck so as to produce a shadow image of an edge of said element; (d) an elongated sensor means located below said light source and the outer edge of said element and positioned to receive said shadow image; (e) means for processing the output from said sensor means to produce quadrature signal data relative to the actual position of the edge of said element; (f) means in said controller for synchronizing quadrature signals from said chuck motor and said sensor means for determining the location of said fiducial on said element and its geometric center relative to said chuck; and (g) optical means between said light source and said sensor means for optimizing the demarcation between light and shadow on said sensor means, wherein said optical means comprises first and second pairs of plano-convex lens which are spaced apart between said light source and said sensor means.
2. The system of claim 1 wherein said sensor means comprises a charge coupled device having a plurality of pixels which provide an output when exposed to light.
3. The system of claim 2 wherein the output from said sensor means provides a digital 1 for pixels exposed to light and a digital 0 for pixels within the shadow area and not exposed to light.
4. The system of claim 1 wherein said optical means further comprises a light stop between said first and second lens pairs for providing an aperture for light rays between lens pairs while eliminating extraneous ambient light.
5. The system of claim 1 wherein said means for processing the output from said sensor means comprises: a data processor means; a clocking means for establishing data cycles; and programmable logic means for counting the number of pixels exposed to light in a cycle; subtracting the number of said pixels from the number of pixels exposed to light in a previous cycle to provide a net number; and converting the net number to quadrature signals for said controller.
6. The system of claim 1 wherein said machine controller comprises a logic section and an amplifier section for controlling three axis motors for said robot and also said rotary chuck motor.
7. The system of claim 1 wherein the arm of said robot is movable by said controller in the (r) radial direction, the (.crclbar.) horizontal direction and the (z) vertical direction, and said end effector has finger portions equally spaced from opposite sides of its longitudinal centerline.
8. The system described in claim 1 wherein said disk like element is a semiconductor wafer.
9. The system described in claim 8 wherein said controller includes means for rotating the wafer by said vacuum chuck so that said fiducial is at a predetermined location thereon before the wafer is removed from the chuck by a robot end effector.
10. The system described in claim 1 wherein said controller includes means for computing an offset angle relative to the robot vertical axis from the center of said wafer to the center of said vacuum chuck; and means for controlling the .crclbar. axis motor of said robot to move said robot arm by the amount of said offset angle so that said wafer will be precisely centered on an end effector when the robot removes the wafer from the vacuum chuck.
11. A method for determining the position of a fiducial on the edge of a circular wafer retained on a rotary chuck with respect to the rotary axis of the chuck comprising the steps of: (a) rotating the wafer by said chuck; (b) tracking the position of the wafer's edge as the wafer is rotated to produce wafer edge position data points at time intervals; (c) converting the edge position data to quadrature position data and furnishing it to a controller; (d) processing the edge position data in the controller using a cross correlation procedure in conjunction with an ideal fiducial curve to provide the precise position of the fiducial with respect to the chuck axis, wherein said fiducial is a notch and the controller processing steps include: (i) comparing one notch width of scanned data with a known given ideal notch geometry; (ii) providing a cross-correlation of the ideal notch with the acquired notch position data by summing the product of each data point and a corresponding point in an ideal notch curve; (iii) providing a lookup table for the ideal notch curve; (iv) calculating an index into said table using the angle of said chuck axis for each data point; (v) establishing a cross-correlation threshold; and (vi) marking the location of the notch when the cross-correlation value falls below the threshold.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
April 16, 1999
August 14, 2001
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.